The present invention relates to a piezoelectric ceramics transformer, and particularly to a multi-output composite piezoelectric ceramics transformer with expansion vibration mode.
The piezoelectric ceramics transformer of the prior art mainly consists of single layered or multi-layered piezoelectric ceramics fabricated by only one sintering process. Various parameters of the primary and the secondary of a piezoelectric ceramics assembly of the transformer should be adjusted to meet the matching requirements of the different parameters of the inputs and the outputs, especially for a step down piezoelectric ceramics transformer. Therefore, different types of piezoelectric materials and complicated constructions should be employed in designing the primary and secondary assemblies of the piezoelectric transformer. However, different types of piezoelectric materials require different sintering conditions. It is extremely difficult to fabricate an ideal piezoelectric ceramics transformer in only one sintering process.
In the past, a step down piezoelectric ceramics transformer is driven by vibration in its thickness direction so that piezoelectric property of d33 of the piezoelectric materials can be used and highly operating frequency can be obtained simultaneously. However, the stress distribution induced by the vibration in the thickness direction results in the technical difficulties in arranging the primary and the secondary assemblies of the piezoelectric ceramics transformer. Moreover, the stress distribution also gives rise to a charge cancellation and none-equilibrium charge distribution, which, in turn, inversely affects the performance of the piezoelectric transformer; hence, satisfactory outputs cannot be obtained.
On the other hand, though there is an isolation layer between the primary and the secondary assemblies of the piezoelectric ceramics transformer, the isolated capacitance caused by the isolation layer is too large so that only AC channels can be formed, of which the function of isolation layer is only to isolate DC, and appropriate isolation cannot be achieved when the piezoelectric ceramics transformer operates at a high frequency. Some isolation layers may reduce the capacitance between the primary and the secondary assemblies, but it causes the difficulty in stress transport, an increase of power consumption and a decrease of power output etc. Because the size of the piezoelectric ceramics transformer is rather small and the thickness is only a few millimeters, even insulation property of the inner isolation layer is extremely high, the isolation may be invalidated for being breakdown due to the narrow spacing between the primary and the secondary assemblies, as well as the surface charge diffusion. Consequently, damage of the instrument and personal injuries may occur.
The piezoelectric ceramics transformer of the prior art, working in single output mode, fails to meet the multi-output requirements of many electronics equipment, which considerably limits the application of the piezoelectric ceramics transformer.
The object of the present invention is to provide a multi-output piezoelectric ceramics transformer with expansion vibration mode that solves the above problems, and has the character of easy adjustment for the purpose of matching various parameters of the primary and the secondary assemblies, high output power and high conversion efficiency, reliable isolation between the primary and the secondary assemblies, and satisfactory performance to meet the requirements of the applications of step down power supply.
To achieve the above object, the present invention provides a multi-output composite piezoelectric ceramics transformer, which is driven in expansion vibration mode and has the primary and the secondary piezoelectric ceramics assemblies; characters in that a multi-output composite piezoelectric ceramics transformer with expansion vibration mode comprises a high polymer bonding structure, an insulating isolative structure and an electrodes lead structure, the primary and the secondary piezoelectric ceramics assemblies as well as the isolation layers of a insulating isolative structure are laminated one by one and bonded firmly with polymer adhesives to form a sandwiched structure. The electrodes are leaded out by electrodes lead structure of the piezoelectric ceramics assemblies to form the external input and output terminals. The exterior surfaces of both the piezoelectric ceramics assemblies and electrode lead structure are coated with film of polymer insulating materials which together with isolation layers, form a continuous and integrated insulating isolation structure of the transformer.
The piezoelectric ceramic transformer comprises multiple outputs. The secondary piezoelectric ceramic subassemblies are isolated from each other by an isolation plate in the independent multi-output subassemblies. The adjacent piezoelectric ceramic plates are polarized in opposite directions to each other in a secondary subassembly. Two adjacent piezoelectric ceramic plates, which are at the interface between the positive and the negative output subassemblies, respectively, and which share a common grounding electrode, are arranged in accordance with the same polarization directions. The adjacent piezoelectric ceramic plates in each one of the secondary subassemblies are polarized in opposite directions to each other. All lead side electrodes of surface electrodes which are in a positive output piezoelectric ceramic subassembly and the polarization directions thereof are the same as that of a electrode which is in a negative output piezoelectric ceramic subassembly and adjacent to the positive output piezoelectric ceramic subassembly, and connected by the lead electrode structure. These electrodes are connected with the lead side electrodes of surface electrodes which are in the negative output piezoelectric ceramic subassembly and the polarization directions thereof are the same as that of a electrode which is in a positive output piezoelectric ceramic subassembly and adjacent to the negative output piezoelectric ceramic subassembly. The connected electrodes form a common grounding electrode. All other side electrodes of the positive or the negative output subassemblies are lead out by a lead electrode structure, to form the other electrodes of the positive or the negative outputs, respectively.
The sandwiched structure is formed between the primary and the secondary assemblies of the transformer constituted with the polymer composite structure and the multi-output composite piezoelectric ceramics with expansion vibration mode of this invention, and the primary piezoelectric ceramics assembly can be divided into two identical assemblies, each of which is located on the top and bottom sides of the transformer respectively, and a secondary piezoelectric ceramics assembly is located in the middle of the transformer between two primary assemblies. The upper and lower surfaces of the secondary piezoelectric ceramics assembly are joined to the lower and upper surfaces of the two primary piezoelectric assemblies by the isolation layers, respectively, furthermore all piezoelectric ceramics assemblies and the isolation layers are tightly bonded with the polymer bonding structure to form a sandwiched structure. Alternatively, the structure of the transformer of this invention can also be formed by inserting the primary piezoelectric assembly in the middle of the transformer while the two secondary piezoelectric ceramics assemblies are positioned on both sides of the primary piezoelectric ceramics assembly. The sandwiched structure thereof effectively eliminates the distortion vibration possibly caused by the difference between the damping states of the primary and the secondary piezoelectric ceramics assemblies, and ensures that the transformer vibrates in a single expansion vibration mode.
The insulating isolative structure of this invention comprises the isolation layer and the insulating films. The isolation layer is positioned between the primary and the secondary assemblies, and if required, the isolation layers can also be inserted between different secondary subassemblies in the multi-output piezoelectric ceramics transformer. The isolation layer that is a plate made of a ceramic, a glass or a film of composite materials with a diameter slightly bigger than that of the piezoelectric ceramics assembly, play the part of isolation inside the piezoelectric ceramics transformer. The modulus of elasticity of the isolation layers should be in the range of one tenth to ten times of that of the piezoelectric ceramics material thereof, so that the vibrating status of the transformer cannot be inversely affected by the isolation layers. Insulating film covers the exterior surfaces of both the primary and the secondary assemblies as well as the exposed exterior surfaces of lead electrode structure and bonds with the isolation layers, therefore, combined with the isolation layers, the insulating film wraps and bonds the entire piezoelectric ceramics assemblies and forms a compact insulating isolative structure, which effectively protects the piezoelectric ceramics transformer from insulation failures caused by various factors, such as the internal voltage breakdown, the external voltage breakdown resulting from the air, or the surface electric leakage.
The insulating materials which are applieded in the transformer by the processing of spraying or painting are made of a variety of polymer materials, such as epoxy resin, phenolic aldehyde resin, urea-formaldehyde resin, polyamino resin, polyester resin, and polyimide resin.
When the techniques of the present invention are adopted, the composite structure and the multi-output of the transformer make it possible to improve performance of the transformer in many aspects, such as, easy matching of the parameters of both the primary and the secondary assemblies, high output power, high conversion efficiency, reliable isolation of the individual piezoelectric ceramics assembly, and ability to meet the requirements of the step down power supply in the practical applications.